Final answer:
The threshold frequency is the minimum frequency of light necessary to eject electrons from a metal, a concept critical to understanding the photoelectric effect. Light below this frequency won't eject electrons, while light at or above it will, with electron kinetic energy increasing with higher frequencies.
Step-by-step explanation:
When discussing the threshold frequency vo, we refer to the minimum frequency of light required to eject electrons from the surface of a metal. According to the equation E = hv, where E represents the minimum energy needed to eject an electron and h is Planck's constant, light with a frequency below vo cannot provide enough energy to overcome the work function, the energy needed to release an electron from the metal. Therefore, no electrons are ejected unless the frequency of the incoming light matches or exceeds vo.
When light with a frequency equal to or greater than the threshold frequency strikes the metal, electrons are ejected. This photoelectric effect was an important discovery that helped to establish the quantum theory of light. As the frequency increases beyond the threshold frequency, the ejected electrons gain greater kinetic energy but not greater numbers. Conversely, increases in light intensity above the threshold frequency result in more ejected electrons, but without a change in their kinetic energy. This reveals the particle nature of light, where each photon must have enough energy, determined by its frequency, to eject a single electron.
For example, metals like potassium require a specific amount of energy expressed in electron volts (eV) for electron ejection to occur. This is a critical point in understanding the photoelectric effect: only light with sufficient photon energy (as determined by a frequency higher than the threshold frequency) will cause electron emission from the metal surface.